Good observation. The fix is surprisingly simple: 
  sort {
    ## Compare through the shorter only
    for (0..(@$a>@$b ? $#{$b} : $#{$a})) {
      return $a->[$_] <=> $b->[$_] || next
    }
    ## If no difference, the longer array is first
    @$b <=> @$a;

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In reply to Re^4: sort by a multiple columns by Roy Johnson
in thread sort by a multiple columns by johnnywang

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